The gammadelta T cell subset is an important component of the intestinal immune system, yet little is known regarding its role in the host's interaction with microbial pathogens and parasites in the gut. In addition, little is known concerning the cell surface molecules and associated peptides with which they interact. In this study we will investigate the identity of the cell surface molecules recognized by gammadelta T cells. As a model system we will clone the H-2TL region- encoded molecule recognized by the gammadelta T cell clone, G8. A demonstration that the gene encodes the correct ligand will be performed by transfection into mouse and human fibroblasts. Both polyclonal and monoclonal antibodies specific for the molecule will be prepared and used to determine the tissue distribution of the TL molecule. The antibodies will also be used to isolate the TL molecule in order to purify the peptides that are bound. We will attempt to determine whether the character of the peptides differs from those present on MHC class I molecules, and in particular, we will be interested to know whether members of the heat shock family of proteins are represented before, or after heat shock induction. In order to define the peptide that binds to the TL molecule and contributes to the determinant recognized by G8, we will express the TL molecule in insect cells. Previous studies have shown that these MHC class I molecules are "empty" and thus we will use these cells to test peptide fractions for functional activity. For a complete characterization of the TL molecule, in collaboration, we will investigate its three dimensional structure by x-ray crystallography. In order to understand the role of H-2TL region-encoded molecules in the development and function of gammadelta T cells, we will express these molecules in transgenic mice. We will use different promoters that direct distinct patterns of tissue expression, and then analyze the gammadelta T cell populations present in different lymphoid and non- lymphoid compartments. The studies outlined in this proposal will help to clarify the role of gammadelta T cells in the induction of immune responses. Since gammadelta T cells compose a large percentage of the lymphoid cells in the intestinal epithelium, these studies are particularly important for an understanding of mucosal immunology.